Micro-electro-mechanical switches are operated by an electrostatic charge, thermal, piezoelectric or other actuation mechanism. Application of an electrostatic charge to a control electrode in the MEMS causes the switch to close, while removal of the electrostatic charge on the control electrode, allowing the mechanical spring restoration force of the armature to open the switch. Although these MEMS switches work problems have prevented their more widespread use.
For example, one problem with cantilever type MEMS is that they often freeze into a closed position due to a phenomenon known as stiction. These cantilever type MEMS may be actuated by electrostatic forces, however there is no convenient way to apply a force in the opposite direction to release the MEMS to the open position.
One solution to this problem is a design which uses electrostatic repulsive forces to force apart MEMS contacts, such as the one disclosed in U.S. Pat. No. 6,127,744 to R. Streeter et al. which is herein incorporated by reference. In this design, the improved switch includes an insulating substrate, a conductive contact, a cantilever support, a first conductive surface and a cantilever beam. Additionally, a first control surface is provided on the lower surface of and is insulated from the beam by a layer of insulation. A second control surface is disposed over and is separated from the first conductive surface by a layer of insulative material. A variable capacitor is formed by the two control surfaces and the dielectric between them. This capacitor must be considered in addition to the capacitors formed by the first control surface, the layer of insulation and the beam and by the second control surface, the layer of insulation and the first conductive surface.
Unfortunately, there are drawbacks to this design. As discussed above, the additional layers used for attraction or repulsion charge form capacitors which require additional power for operation and thus impose a serious limitation on this type of design. These additional layers also add mass that limits the response time of the switch. Further, this design results in a variable parasitic capacitor between the cantilever beam and contact post.